DNA Replication 12th Grade PDF

12th grade DNA Replication Events, Enzymes, & Editing Meselson-Stahl Experiment Process of DNA Replication Let’s quickly review the steps and enzymes involved.  Eukaryotic DNA is long = many Replication Bubbles Multiple replication origins are need...

12th grade DNA Replication Events, Enzymes, & Editing Meselson-Stahl Experiment Process of DNA Replication Let’s quickly review the steps and enzymes involved.  Eukaryotic DNA is long = many Replication Bubbles Multiple replication origins are needed to ensure DNA is replicated in a practical amount of time.  ?? In Eukaryotes, new DNA is made at a rate of about 50 base pairs per ________ ______ (#) second (time unit) at each replication fork. Step 1: Strand Separation Helicase Topoisomerases Single-strand A replication enzyme A class of enzymes that binding protein that separates and relieve tension caused A replication enzyme unwinds the DNA by the unwinding of that prevents parent strands parent DNA (allows the DNA strands from strands to untwist and annealing to each other then rejoin) once they have been separated by helicase Where would topoisomerase be found in this diagram? Step 2: Building Complementary Strands RNA Primase DNA Polymerase III Leading Strand A replication enzyme that A prokaryotic replication The DNA strand that is produces RNA primers. enzyme that builds new copied in the direction DNA strands from toward the replication fork nucleotides. (5’ to 3’) Lagging Strand Okazaki Fragment The DNA strand that is The piece of new DNA on copied in the direction away the lagging strand from the replication fork Step 2: Building Complementary Strands DNA Polymerase I DNA Ligase A prokaryotic replication An enzyme that catalyzes enzyme that fills in gaps in the formation of a the lagging strand between phosphodiester bond Okazaki fragments; also between two DNA strands proofreads the final strands (between Okazaki fragments) Step 3: Dealing with Errors DNA Polymerase II A prokaryotic replication enzyme that repairs damage to DNA, including damage that occurs between replication events  Preserving Accuracy in DNA Occasionally, errors occur in DNA replication; about 1 per every 100,000 nucleotides DNA Pol I and DNA Pol II proofread newly synthesized sections of the DNA strand and replace incorrect nucleotides Another safenet mechanism is called mismatch repair where RNA polymerase II & other molecules recognize the error, excise it, and then refill it with the correct nucleotides: DNA Replication in Prokaryotes & Eukaryotes Most of what we know comes from the study of bacteria (prokaryotes). However, research has shown that DNA replication in eukaryotes is essentially the same. BUT, there are differences due to the differences in the genomic content and structure.  DNA Replication Differences Prokaryotes Eukaryotes One replication origin Thousands of origins One replication bubble Many replication bubbles DNA Polymerases DNA Polymerases more varied No loss of sequence due to Linear DNA strands leads to loss of DNA replication sequence at very ends Telomeres - repetitive sequences of DNA, evolved to slow down the loss of important genetic information. Telomerase re-extends the lost sequence The loss of DNA during every cycle of replication causes chromosomes to continually shorten and can lead to the loss or damage of important genes. To prevent the loss of essential coding regions of DNA, zones of repetitive, non-coding sequences are found at the ends of eukaryotic chromosomes. These sequences are called telomeres. Every time that DNA replicates, part of its telomeres are lost, but the coding regions of DNA remain complete.